Micro-electromechanical assembly that incorporates a covering formation for a micro-electromechanical device

ABSTRACT

A micro-electromechanical assembly includes a substrate that incorporates drive circuitry. A micro-electromechanical device is positioned on the substrate and is electrically connected to the drive circuitry to be driven by electrical signals generated by the drive circuitry. A covering formation is positioned on the substrate and is configured to enclose the micro-electromechanical device.

This is a Continuation Application of U.S. Ser. No. 10/302,556 filed onNov. 23, 2002 now U.S. Pat. No. 6,666,543.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

FIELD OF THE INVENTION

This invention relates to a micro-electromechanical assembly. Moreparticularly, this invention relates to a micro-electromechanicalassembly which incorporates a covering formation for amicro-electromechanical device.

REFERENCED PATENT APPLICATIONS

The following patents/patent applications are incorporated by reference.

6,227,652 6,213,588 6,213,589 6,231,163 6,247,795 09/113,099 6,244,6916,257,704 09/112,778 6,220,694 6,257,705 6,247,794 6,234,610 6,247,7936,264,306 6,241,342 6,247,792 6,264,307 6,254,220 6,234,611 09/112,80809/112,809 6,239,821 09/113,083 6,247,796 09/113,122 09/112,79309/112,794 09/113,128 09/113,127 6,227,653 6,234,609 6,238,040 6,188,4156,227,654 6,209,989 6,247,791 09/112,764 6,217,153 09/112,767 6,243,11309/112,807 6,247,790 6,260,953 6,267,469 09/425,419 09/425,41809/425,194 09/425,193 09/422,892 09/422,806 09/425,420 09/422,89309/693,703 09/693,706 09/693,313 09/693,279 09/693,727 09/693,70809/575,141 09/113,053 09/855,094 09/854,762 09/854,715 09/854,83009/854,714 09/854,703 09/855,093 09/854,815 09/854,825 09/864,37709/864,380 09/900,178 09/864,379 09/864,378 09/864,334 09/864,33209/864,343 09/864,342 09/866,786 09/874,757 09/900,174 09/900,16009/900,175 09/900,177 09/900,159 09/900,176 09/922,274 09/922,27509/922,158 09/922,159 09/922,036 09/922,047 09/922,029 09/922,20709/922,112 09/922,105 09/942,549 09/942,605 09/942,548 09/942,60309/942,604

BACKGROUND OF THE INVENTION

As set out in the above referenced applications/patents, the Applicanthas spent a substantial amount of time and effort in developingprintheads that incorporate micro electromechanical system (MEMS)—basedcomponents to achieve the ejection of ink necessary for printing.

As a result of the Applicant's research and development, the Applicanthas been able to develop printheads having one or more printhead chipsthat together incorporate up to 84 000 nozzle arrangements. TheApplicant has also developed suitable processor technology that iscapable of controlling operation of such printheads. In particular, theprocessor technology and the printheads are capable of cooperating togenerate resolutions of 1600 dpi and higher in some cases. Examples ofsuitable processor technology are provided in the above referencedpatent applications/patents.

The Applicant has overcome substantial difficulties in achieving thenecessary ink flow and ink drop separation within the ink jetprintheads. A number of printhead chips that the Applicant has developedincorporate nozzle arrangements that each have a nozzle chamber with anink ejection member positioned in the nozzle chamber. The ink ejectionmember is then displaceable within the nozzle chamber to eject ink fromthe nozzle chamber.

A particular difficulty that the Applicant addresses in the presentinvention is to do with the delicate nature of the various componentsthat comprise each nozzle arrangement of the printhead chip. In theabove referenced matters, the various components are often exposed as arequirement of their function. On the MEMS scale, the various componentsare well suited for their particular tasks and the Applicant has foundthem to be suitably robust.

However, on a macroscopic scale, the various components can easily bedamaged by such factors as handling and ingress of microscopic detritus.This microscopic detritus can take the form of paper dust.

It is therefore desirable that a means be provided whereby thecomponents are protected. Applicant has found, however, that it isdifficult to fabricate a suitable covering for the components whilestill achieving a transfer of force to an ink-ejecting component andefficient sealing of a nozzle chamber.

The Applicant has conceived this invention in order to address thesedifficulties.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provides amicro-electromechanical assembly that comprises

a substrate that incorporates drive circuitry;

a micro-electromechanical device that is positioned on the substrate andis electrically connected to the drive circuitry to be driven byelectrical signals generated by the drive circuitry; and

a covering formation that is positioned on the substrate and isconfigured to enclose the micro-electromechanical device.

The covering formation may include sidewalls that extend from thesubstrate and a roof wall that spans the substrate.

The micro-electromechanical device may include an elongate actuator thathas a fixed end that is connected to the substrate so that the actuatorcan receive an electrical signal from the drive circuitry and a movableend, the actuator being configured so that the movable end is displacedrelative to the substrate on receipt of the electrical signal.

A motion-transmitting structure may be fast with the movable end of theactuator. The motion-transmitting structure may be connected to aworking member so that movement of the actuator is translated to theworking member. The motion-transmitting structure may define part of theroof wall and may be spaced from a remaining part of the roof wall toallow for movement of the motion-transmitting structure.

The roof wall may define a cover that spans the walls to cover theelongate actuator. The motion-transmitting structure may be shaped sothat the cover and the motion-transmitting structure define generallyco-planar surfaces that are spaced from, and generally parallel to thesubstrate. An opening may be defined between the cover and themotion-transmitting surface to facilitate relative displacement of thecover and the motion-transmitting surface.

The actuator may include at least one elongate actuator arm of aconductive material that is capable of thermal expansion to performwork. The actuator arm may have an active portion that defines a heatingcircuit that is connected to the drive circuitry layer to be resistivelyheated on receipt of the electrical signal from the drive circuitrylayer and subsequently cooled on termination of the signal, and apassive portion which is insulated from the drive circuitry layer, theactive and passive portions being positioned with respect to each otherso that the arm experiences differential thermal expansion andcontraction reciprocally to displace the movable end of the actuator.

The motion-transmitting structure may define a lever mechanism and mayhave a fulcrum formation that is fast with the substrate and pivotalwith respect to the substrate and a lever arm formation mounted on thefulcrum formation. An effort formation may be connected between themovable end of the actuator and the lever arm formation and a loadformation may be connected between the lever arm formation and theworking member.

The lever arm formation, the cover and the walls may define a unitarystructure with the lever arm formation being connected to the walls witha pair of opposed torsion formations that are configured to twist as thelever formation is displaced.

The sidewalls may include nozzle chamber walls, the roof wall defining anozzle chamber together with the nozzle chamber walls and themotion-transmitting structure. The roof wall may define an ejection portin fluid communication with the nozzle chamber, the working member beingin the form of a fluid ejection device that is positioned in the nozzlechamber, such that displacement of the working member results inejection of fluid in the nozzle chamber from the ejection port. Thesubstrate may define a fluid inlet channel in fluid communication withthe nozzle chamber to supply the nozzle chamber with fluid.

According to a second aspect of the invention, there is provided aprinthead chip for an inkjet printhead, the printhead chip comprising

a substrate; and

a plurality of nozzle arrangements that is positioned on the substrate,each nozzle arrangement comprising

nozzle chamber walls and a roof that define a nozzle chamber with theroof defining an ink ejection port in fluid communication with thenozzle chamber;

an ink-ejecting member that is positioned in the nozzle chamber, theink-ejecting member being displaceable towards and away from the inkejection port so that a resultant fluctuation in ink pressure within thenozzle chamber results in an ejection of ink from the ink ejection port;

at least one work-transmitting structure that is displaceable withrespect to the substrate and is connected to the ink-ejecting member sothat displacement of the work transmitting structure results indisplacement of the ink-ejecting member;

an actuator that is connected to the work-transmitting structure, theactuator being capable of displacing the work transmitting structureupon receipt of an electrical drive signal; and

air chamber walls and a covering formation that is positioned over theactuator, the air chamber walls and the covering formation defining anair chamber in which the actuator is positioned, the roof, the worktransmitting structure and the covering formation together defining aprotective structure positioned in a common plane.

The invention is now described, by way of example, with reference to theaccompanying drawings. The following description is not intended tolimit the broad scope of the above summary.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 shows a sectioned, three dimensional view of a nozzle arrangementof a printhead chip, in accordance with the invention, for an inkjetprinthead; and

FIG. 2 shows a three dimensional view of the nozzle arrangement of FIG.1.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings, reference numeral 10 generally indicates a nozzlearrangement for a first embodiment of an ink jet printhead chip, inaccordance with the invention.

The nozzle arrangement 10 is one of a plurality of such nozzlearrangements formed on a silicon wafer substrate 12 to define theprinthead chip of the invention. As set out in the background of thisspecification, a single printhead can contain up to 84 000 such nozzlearrangements. For the purposes of clarity and ease of description, onlyone nozzle arrangement is described. It is to be appreciated that aperson of ordinary skill in the field can readily obtain the printheadchip by simply replicating the nozzle arrangement 10 on the wafersubstrate 12.

The printhead chip is the product of an integrated circuit fabricationtechnique. In particular, each nozzle arrangement 10 is the product of aMEMS—based fabrication technique. As is known, such a fabricationtechnique involves the deposition of functional layers and sacrificiallayers of integrated circuit materials. The functional layers are etchedto define various moving components and the sacrificial layers areetched away to release the components. As is known, such fabricationtechniques generally involve the replication of a large number ofsimilar components on a single wafer that is subsequently diced toseparate the various components from each other. This reinforces thesubmission that a person of ordinary skill in the field can readilyobtain the printhead chip of this invention by replicating the nozzlearrangement 10.

An electrical drive circuitry layer 14 is positioned on the siliconwafer substrate 12. The electrical drive circuitry layer 14 includesCMOS drive circuitry. The particular configuration of the CMOS drivecircuitry is not important to this description and has therefore beenshown schematically in the drawings. Suffice to say that it is connectedto a suitable microprocessor and provides electrical current to thenozzle arrangement 10 upon receipt of an enabling signal from saidsuitable microprocessor. An example of a suitable microprocessor isdescribed in the above referenced patents/patent applications. Itfollows that this level of detail will not be set out in thisspecification.

An ink passivation layer 16 is positioned on the drive circuitry layer14. The ink passivation layer 16 can be of any suitable material, suchas silicon nitride.

The nozzle arrangement 10 includes nozzle chamber walls 18 positioned onthe ink passivation layer 16. A roof 20 is positioned on the nozzlechamber walls 18 so that the roof 20 and the nozzle chamber walls 18define a nozzle chamber 22. The nozzle chamber walls 18 include a distalend wall 24, a proximal end wall 26 and a pair of opposed sidewalls 28.An ink ejection port 30 is defined in the roof 20 to be in fluidcommunication with the nozzle chamber 22. The roof 20 defines a nozzlerim 32 and a recess 34 positioned about the rim 32 to accommodate inkspread.

The walls 18 and the roof 20 are configured so that the nozzle chamber22 is rectangular in plan.

A plurality of ink inlet channels 36, one of which is shown in thedrawings, are defined through the substrate 12, the drive circuitrylayer 14 and the ink passivation layer 16. The ink inlet channel 36 isin fluid communication with the nozzle chamber 18 so that ink can besupplied to the nozzle chamber 18.

The nozzle arrangement 10 includes a work-transmitting structure in theform of a lever mechanism 38. The lever mechanism 38 includes an effortformation 40, a fulcrum formation 42 and a load formation 44. Thefulcrum formation 42 is interposed between the effort formation 40 andthe load formation 44.

The fulcrum formation 42 is fast with the ink passivation layer 16. Inparticular, the fulcrum formation 42 is composite with a primary layer46 and a secondary layer 48. The layers 46, 48 are configured so thatthe fulcrum formation 42 is resiliently deformable to permit pivotalmovement of the fulcrum formation 42 with respect to the substrate 12.The layers 46, 48 can be of a number of materials that are used inintegrated circuit fabrication. The Applicant has found that titaniumaluminum nitride (TiAlN) is a suitable material for the layer 46 andthat titanium is a suitable material for the layer 48.

The load formation 44 defines part of the proximal end wall 26. The loadformation 44 is composite with a primary layer 50 and a secondary layer52. As with the fulcrum formation 42, the layers 50, 52 can be of any ofa number of materials that are used in integrated circuit fabrication.However, as set out above, the nozzle arrangement 10 is fabricated byusing successive deposition and etching steps. It follows that it isconvenient for the layers 50, 52 to be of the same material as thelayers 46, 48. Thus, the layers 50, 52 can be of TiAlN and titanium,respectively.

The nozzle arrangement 10 includes an ink-ejecting member in the form ofan elongate rectangular paddle 54. The paddle 54 is fixed to the loadformation 44 and extends towards the distal end wall 24. Further, thepaddle 54 is dimensioned to correspond generally with the nozzle chamber22. It follows that displacement of the paddle 54 towards and away fromthe ink ejection port 30 with sufficient energy results in the ejectionof an ink drop from the ink ejection port. The manner in which dropejection is achieved is described in detail in the above referencedpatents/applications and is therefore not discussed in any detail here.

To facilitate fabrication, the paddle 54 is of TiAlN. In particular, thepaddle 54 is an extension of the layer 50 of the load formation 44 ofthe lever mechanism 38.

The paddle 54 has corrugations 56 to strengthen the paddle 54 againstflexure during operation.

The effort formation 40 is also composite with a primary layer 58 and asecondary layer 60.

The layers 58, 60 can be of any of a number of materials that are usedin integrated circuit fabrication. However, as set out above, the nozzlearrangement 10 is fabricated by using successive deposition and etchingsteps. It follows that it is convenient for the layers 58, 60 to be ofthe same material as the layers 46, 48. Thus, the layers 58, 60 can beof TiAlN and titanium, respectively.

The nozzle arrangement 10 includes an actuator in the form of a thermalbend actuator 62. The thermal bend actuator 62 is of a conductivematerial that is capable of being resistively heated. The conductivematerial has a coefficient of thermal expansion that is such that, whenheated and subsequently cooled, the material is capable of expansion andcontraction to an extent sufficient to perform work on a MEMS scale.

The thermal bend actuator 62 can be any of a number of thermal bendactuators described in the above patents/patent applications. In oneexample, the thermal bend actuator 62 includes an actuator arm 64 thathas an active portion 82 and a passive portion. The active portion 82has a pair of inner legs 66 and the passive portion is defined by a legpositioned on each side of the pair of inner legs 66. A bridge portion68 interconnects the active legs 66 and the passive legs. Each leg 66 isfixed to one of a pair of anchor formations in the form of activeanchors 70 that extend from the ink passivation layer 16. Each activeanchor 70 is configured so that the legs 66 are electrically connectedto the drive circuitry layer 14.

Each passive leg is fixed to one of a pair of anchor formations in theform of passive anchors 88 that are electrically isolated from the drivecircuitry layer 14.

Thus, the legs 66 and the bridge portion 68 are configured so that whena current from the drive circuitry layer 14 is set up in the legs 66,the actuator arm 64 is subjected to differential heating. In particular,the actuator arm 64 is shaped so that the passive legs are interposedbetween at least a portion of the legs 66 and the substrate 12. It willbe appreciated that this causes the actuator arm 64 to bend towards thesubstrate 12.

The bridge portion 68 therefore defines a working end of the actuator62. In particular, the bridge portion 68 defines the primary layer 58 ofthe effort formation 40. Thus, the actuator 62 is of TiAlN. TheApplicant has found this material to be well suited for the actuator 62.

The lever mechanism 38 includes a lever arm formation 72 positioned on,and fast with, the secondary layers 48, 52, 60 of the fulcrum formation42, the load formation 44 and the effort formation 40, respectively.Thus, reciprocal movement of the actuator 62 towards and away from thesubstrate 12 is converted into reciprocal angular displacement of thepaddle 54 via the lever mechanism 38 to eject ink drops from the inkejection port 30.

Each active anchor 70 and passive anchor is also composite with aprimary layer 74 and a secondary layer 76. The layers 74, 76 can be ofany of a number of materials that are used in integrated circuitfabrication. However, in order to facilitate fabrication, the layer 74is of TiAlN and the layer 76 is of titanium.

A cover formation 78 is positioned on the anchors 70, 88 to extend overand to cover the actuator 62. Air chamber walls 90 extend between theink passivation layer 16 and the cover formation 78 so that the coverformation 78 and the air chamber walls 90 define an air chamber 80.Thus, the actuator 62 and the anchors are positioned in the air chamber80.

The cover formation 78, the lever arm formation 72 and the roof 20 arein the form of a unitary protective structure 92 to inhibit damage tothe nozzle arrangement 10.

The protective structure 92 can be one of a number of materials that areused in integrated circuit fabrication. The Applicant has found thatsilicon dioxide is particularly useful for this task.

It will be appreciated that it is necessary for the lever arm formation72 to be displaced relative to the cover formation 78 and the roof 20.It follows that the cover formation 78 and the lever arm formation 72are demarcated by a slotted opening 94 in fluid communication with theair chamber 80. The roof 20 and the lever arm formation 72 aredemarcated by a slotted opening 96 in fluid communication with thenozzle chamber 22.

The lever arm formation 72 and the roof 20 together define ridges 98that bound the slotted opening 96. Thus, when the nozzle chamber 22 isfilled with ink, the ridges 98 define a fluidic seal during inkejection. The ridges 98 serve to inhibit ink spreading by providingsuitable adhesion surfaces for a meniscus formed by the ink.

The slotted openings 94, 96 demarcate a torsion formation 100 defined bythe protective structure 92. The torsion formation 100 serves to supportthe lever mechanism 38 in position. Further, the torsion formation 100is configured to experience twisting deformation in order to accommodatepivotal movement of the lever mechanism 38 during operation of thenozzle arrangement 10. The silicon dioxide of the protective structure92 is resiliently flexible on a MEMS scale and is thus suitable for suchrepetitive distortion.

Applicant believes that this invention provides a printhead chip that isresistant to damage during handling. The primary reason for this is theprovision of the protective structure 92, which covers the movingcomponents of the nozzle arrangements of the printhead chip. Theprotective structure 92 is positioned in a common plane. It follows thatwhen a plurality of the nozzle arrangements 10 are positioned togetherto define the printhead chip, the printhead chip presents asubstantially uniform surface that is resistant to damage.

I claim:
 1. A micro-electromechanical assembly that comprises asubstrate that incorporates drive circuitry; a micro-electromechanicaldevice that is positioned on the substrate and is electrically connectedto the drive circuitry to be driven by electrical signals generated bythe drive circuitry; and a covering formation that is positioned on thesubstrate and is configured to enclose the micro-electromechanicaldevice.
 2. An assembly as claimed in claim 1, in which the coveringformation includes sidewalls that extend from the substrate and a roofwall that spans the substrate.
 3. An assembly as claimed in claim 2, inwhich the micro-electromechanical device includes an elongate actuatorthat has a fixed end that is connected to the substrate so that theactuator can receive an electrical signal from the drive circuitry and amovable end, the actuator being configured so that the movable end isdisplaced relative to the substrate on receipt of the electrical signal.4. An assembly as claimed in claim 3, in which a motion-transmittingstructure is fast with the movable end of the actuator, themotion-transmitting structure being connected to a working member sothat movement of the actuator is translated to the working member, themotion-transmitting structure defining part of the roof wall and spacedfrom a remaining part of the roof wall to allow for movement of themotion-transmitting structure.
 5. An assembly as claimed in claim 4, inwhich the roof wall defines a cover that spans the walls to cover theelongate actuator, the motion-transmitting structure being shaped sothat the cover and the motion-transmitting structure define generallyco-planar surfaces that are spaced from, and generally parallel to thesubstrate, an opening being defined between the cover and themotion-transmitting surface to facilitate relative displacement of thecover and the motion-transmitting surface.
 6. A device as claimed inclaim 4, in which the motion-transmitting structure defines a levermechanism and has a fulcrum formation that is fast with the substrateand pivotal with respect to the substrate and a lever arm formationmounted on the fulcrum formation, an effort formation being connectedbetween the movable end of the actuator and the lever arm formation anda load formation being connected between the lever arm formation and theworking member.
 7. A device as claimed in claim 6, in which the leverarm formation, the cover and the walls define a unitary structure withthe lever arm formation being connected to the walls with a pair ofopposed torsion formations that are configured to twist as the leverformation is displaced.
 8. A device as claimed in claim 4, in which thesidewalls include nozzle chamber walls, the roof wall defining a nozzlechamber together with the nozzle chamber walls and themotion-transmitting structure, the roof wall defining an ejection portin fluid communication with the nozzle chamber, the working member beingin the form of a fluid ejection device that is positioned in the nozzlechamber, such that displacement of the working member results inejection of fluid in the nozzle chamber from the ejection port, thesubstrate defining a fluid inlet channel in fluid communication with thenozzle chamber to supply the nozzle chamber with fluid.
 9. An assemblyas claimed in claim 3, in which the actuator includes at least oneelongate actuator arm of a conductive material that is capable ofthermal expansion to perform work, the actuator arm having an activeportion that defines a heating circuit that is connected to the drivecircuitry layer to be resistively heated on receipt of the electricalsignal from the drive circuitry layer and subsequently cooled ontermination of the signal, and a passive portion which is insulated fromthe drive circuitry layer, the active and passive portions beingpositioned with respect to each other so that the arm experiencesdifferential thermal expansion and contraction reciprocally to displacethe movable end of the actuator.